/*
 * Copyright 2014 mango.jfaster.org
 *
 * The Mango Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package org.jfaster.mango.reflect;

import org.jfaster.mango.util.Joiner;
import org.jfaster.mango.util.Objects;
import org.jfaster.mango.util.Primitives;

import java.io.Serializable;
import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Array;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.GenericDeclaration;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Proxy;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.security.AccessControlException;
import java.util.*;
import java.util.concurrent.atomic.AtomicReference;

import javax.annotation.Nullable;

/**
 * Utilities for working with {@link Type}.
 *
 * @author Ben Yu
 */
final public class Types {

    private static final Joiner COMMA_JOINER = Joiner.on(", ").useForNull("null");

    /** Returns the array type of {@code componentType}. */
    static Type newArrayType(Type componentType) {
        if (componentType instanceof WildcardType) {
            WildcardType wildcard = (WildcardType) componentType;
            Type[] lowerBounds = wildcard.getLowerBounds();
            if (lowerBounds.length > 1) {
                throw new IllegalArgumentException("Wildcard cannot have more than one lower bounds.");
            }
            if (lowerBounds.length == 1) {
                return supertypeOf(newArrayType(lowerBounds[0]));
            } else {
                Type[] upperBounds = wildcard.getUpperBounds();
                if (upperBounds.length != 1) {
                    throw new IllegalArgumentException("Wildcard should have only one upper bound.");
                }
                return subtypeOf(newArrayType(upperBounds[0]));
            }
        }
        return JavaVersion.CURRENT.newArrayType(componentType);
    }

    /**
     * Returns a type where {@code rawType} is parameterized by
     * {@code arguments} and is owned by {@code ownerType}.
     */
    static ParameterizedType newParameterizedTypeWithOwner(
            @Nullable Type ownerType, Class<?> rawType, Type... arguments) {
        if (ownerType == null) {
            return newParameterizedType(rawType, arguments);
        }
        // ParameterizedTypeImpl constructor already checks, but we want to throw NPE before IAE
        if (arguments == null) {
            throw new NullPointerException();
        }
        if (rawType.getEnclosingClass() == null) {
            throw new IllegalArgumentException(String.format("Owner type for unenclosed %s", rawType));
        }
        return new ParameterizedTypeImpl(ownerType, rawType, arguments);
    }

    /**
     * Returns a type where {@code rawType} is parameterized by
     * {@code arguments}.
     */
    static ParameterizedType newParameterizedType(Class<?> rawType, Type... arguments) {
        return new ParameterizedTypeImpl(
                ClassOwnership.JVM_BEHAVIOR.getOwnerType(rawType), rawType, arguments);
    }

    /** Decides what owner type to use for constructing {@link ParameterizedType} from a raw class. */
    private enum ClassOwnership {

        OWNED_BY_ENCLOSING_CLASS {
            @Nullable
            @Override
            Class<?> getOwnerType(Class<?> rawType) {
                return rawType.getEnclosingClass();
            }
        },
        LOCAL_CLASS_HAS_NO_OWNER {
            @Nullable
            @Override
            Class<?> getOwnerType(Class<?> rawType) {
                if (rawType.isLocalClass()) {
                    return null;
                } else {
                    return rawType.getEnclosingClass();
                }
            }
        };

        @Nullable abstract Class<?> getOwnerType(Class<?> rawType);

        static final ClassOwnership JVM_BEHAVIOR = detectJvmBehavior();

        private static ClassOwnership detectJvmBehavior() {
            class LocalClass<T> {}
            Class<?> subclass = new LocalClass<String>() {}.getClass();
            ParameterizedType parameterizedType = (ParameterizedType)
                    subclass.getGenericSuperclass();
            for (ClassOwnership behavior : ClassOwnership.values()) {
                if (behavior.getOwnerType(LocalClass.class) == parameterizedType.getOwnerType()) {
                    return behavior;
                }
            }
            throw new AssertionError();
        }
    }

    /**
     * Returns a new {@link TypeVariable} that belongs to {@code declaration} with
     * {@code name} and {@code bounds}.
     */
    static <D extends GenericDeclaration> TypeVariable<D> newArtificialTypeVariable(
            D declaration, String name, Type... bounds) {
        return newTypeVariableImpl(
                declaration,
                name,
                (bounds.length == 0)
                        ? new Type[] { Object.class }
                        : bounds);
    }

    /** Returns a new {@link WildcardType} with {@code upperBound}. */
    static WildcardType subtypeOf(Type upperBound) {
        return new WildcardTypeImpl(new Type[0], new Type[] { upperBound });
    }

    /** Returns a new {@link WildcardType} with {@code lowerBound}. */
    static WildcardType supertypeOf(Type lowerBound) {
        return new WildcardTypeImpl(new Type[] { lowerBound }, new Type[] { Object.class });
    }

    /**
     * Returns human readable string representation of {@code type}.
     * <ul>
     * <li> For array type {@code Foo[]}, {@code "com.mypackage.Foo[]"} are
     * returned.
     * <li> For any class, {@code theClass.getName()} are returned.
     * <li> For all other types, {@code type.toString()} are returned.
     * </ul>
     */
    static String toString(Type type) {
        return (type instanceof Class)
                ? ((Class<?>) type).getName()
                : type.toString();
    }

    @Nullable static Type getComponentType(Type type) {
        if (type == null) {
            throw new NullPointerException();
        }
        final AtomicReference<Type> result = new AtomicReference<Type>();
        new TypeVisitor() {
            @Override void visitTypeVariable(TypeVariable<?> t) {
                result.set(subtypeOfComponentType(t.getBounds()));
            }
            @Override void visitWildcardType(WildcardType t) {
                result.set(subtypeOfComponentType(t.getUpperBounds()));
            }
            @Override void visitGenericArrayType(GenericArrayType t) {
                result.set(t.getGenericComponentType());
            }
            @Override void visitClass(Class<?> t) {
                result.set(t.getComponentType());
            }
        }.visit(type);
        return result.get();
    }

    /**
     * Returns {@code ? extends X} if any of {@code bounds} is a subtype of {@code X[]}; or null
     * otherwise.
     */
    @Nullable private static Type subtypeOfComponentType(Type[] bounds) {
        for (Type bound : bounds) {
            Type componentType = getComponentType(bound);
            if (componentType != null) {
                // Only the first bound can be a class or array.
                // Bounds after the first can only be interfaces.
                if (componentType instanceof Class) {
                    Class<?> componentClass = (Class<?>) componentType;
                    if (componentClass.isPrimitive()) {
                        return componentClass;
                    }
                }
                return subtypeOf(componentType);
            }
        }
        return null;
    }

    private static final class GenericArrayTypeImpl
            implements GenericArrayType, Serializable {

        private final Type componentType;

        GenericArrayTypeImpl(Type componentType) {
            this.componentType = JavaVersion.CURRENT.usedInGenericType(componentType);
        }

        @Override public Type getGenericComponentType() {
            return componentType;
        }

        @Override public String toString() {
            return Types.toString(componentType) + "[]";
        }

        @Override public int hashCode() {
            return componentType.hashCode();
        }

        @Override public boolean equals(Object obj) {
            if (obj instanceof GenericArrayType) {
                GenericArrayType that = (GenericArrayType) obj;
                return Objects.equal(
                        getGenericComponentType(), that.getGenericComponentType());
            }
            return false;
        }

        private static final long serialVersionUID = 0;
    }

    private static final class ParameterizedTypeImpl
            implements ParameterizedType, Serializable {

        private final Type ownerType;
        private final List<Type> argumentsList;
        private final Class<?> rawType;

        ParameterizedTypeImpl(
                @Nullable Type ownerType, Class<?> rawType, Type[] typeArguments) {
            if (rawType == null) {
                throw new NullPointerException();
            }
            if (typeArguments.length != rawType.getTypeParameters().length) {
                throw new IllegalArgumentException();
            }
            disallowPrimitiveType(typeArguments, "type parameter");
            this.ownerType = ownerType;
            this.rawType = rawType;
            this.argumentsList = JavaVersion.CURRENT.usedInGenericType(typeArguments);
        }

        @Override public Type[] getActualTypeArguments() {
            return toArray(argumentsList);
        }

        @Override public Type getRawType() {
            return rawType;
        }

        @Override public Type getOwnerType() {
            return ownerType;
        }

        @Override public String toString() {
            StringBuilder builder = new StringBuilder();
            if (ownerType != null) {
                builder.append(JavaVersion.CURRENT.typeName(ownerType)).append('.');
            }
            builder.append(rawType.getName())
                    .append('<')
                    .append(COMMA_JOINER.join(getTypeNames(argumentsList)))
                    .append('>');
            return builder.toString();
        }

        private List<String> getTypeNames(List<Type> argumentsList) {
            List<String> names = new ArrayList<String>();
            for (Type type : argumentsList) {
                names.add(JavaVersion.CURRENT.typeName(type));
            }
            return names;
        }

        @Override public int hashCode() {
            return (ownerType == null ? 0 : ownerType.hashCode())
                    ^ argumentsList.hashCode() ^ rawType.hashCode();
        }

        @Override public boolean equals(Object other) {
            if (!(other instanceof ParameterizedType)) {
                return false;
            }
            ParameterizedType that = (ParameterizedType) other;
            return getRawType().equals(that.getRawType())
                    && Objects.equal(getOwnerType(), that.getOwnerType())
                    && Arrays.equals(
                    getActualTypeArguments(), that.getActualTypeArguments());
        }

        private static final long serialVersionUID = 0;
    }

    private static <D extends GenericDeclaration> TypeVariable<D> newTypeVariableImpl(
            D genericDeclaration, String name, Type[] bounds) {
        TypeVariableImpl<D> typeVariableImpl =
                new TypeVariableImpl<D>(genericDeclaration, name, bounds);
        @SuppressWarnings("unchecked")
        TypeVariable<D> typeVariable = Reflection.newProxy(
                TypeVariable.class, new TypeVariableInvocationHandler(typeVariableImpl));
        return typeVariable;
    }

    /**
     * Invocation handler to work around a compatibility problem between Java 7 and Java 8.
     *
     * <p>Java 8 introduced a new method {@code getAnnotatedBounds()} in the {@link TypeVariable}
     * interface, whose return type {@code AnnotatedType[]} is also new in Java 8. That means that we
     * cannot implement that interface in source code in a way that will compile on both Java 7 and
     * Java 8. If we include the {@code getAnnotatedBounds()} method then its return type means
     * it won't compile on Java 7, while if we don't include the method then the compiler will
     * complain that an abstract method is unimplemented. So instead we use a dynamic proxy to
     * get an implementation. If the method being called on the {@code TypeVariable} instance has
     * the same name as one of the public methods of {@link TypeVariableImpl}, the proxy calls
     * the same method on its instance of {@code TypeVariableImpl}. Otherwise it throws {@link
     * UnsupportedOperationException}; this should only apply to {@code getAnnotatedBounds()}. This
     * does mean that users on Java 8 who obtain an instance of {@code TypeVariable} from {@link
     * TypeResolver#resolveType} will not be able to call {@code getAnnotatedBounds()} on it, but that
     * should hopefully be rare.
     *
     * <p>This workaround should be removed at a distant future time when we no longer support Java
     * versions earlier than 8.
     */
    private static final class TypeVariableInvocationHandler implements InvocationHandler {
        private static final Map<String, Method> typeVariableMethods;
        static {
            Map<String, Method> map = new HashMap<String, Method>();
            for (Method method : TypeVariableImpl.class.getMethods()) {
                if (method.getDeclaringClass().equals(TypeVariableImpl.class)) {
                    try {
                        method.setAccessible(true);
                    } catch (AccessControlException e) {
                        // OK: the method is accessible to us anyway. The setAccessible call is only for
                        // unusual execution environments where that might not be true.
                    }
                    map.put(method.getName(), method);
                }
            }
            typeVariableMethods = Collections.unmodifiableMap(map);
        }

        private final TypeVariableImpl<?> typeVariableImpl;

        TypeVariableInvocationHandler(TypeVariableImpl<?> typeVariableImpl) {
            this.typeVariableImpl = typeVariableImpl;
        }

        @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            String methodName = method.getName();
            Method typeVariableMethod = typeVariableMethods.get(methodName);
            if (typeVariableMethod == null) {
                throw new UnsupportedOperationException(methodName);
            } else {
                try {
                    return typeVariableMethod.invoke(typeVariableImpl, args);
                } catch (InvocationTargetException e) {
                    throw e.getCause();
                }
            }
        }
    }

    private static final class TypeVariableImpl<D extends GenericDeclaration> {

        private final D genericDeclaration;
        private final String name;
        private final List<Type> bounds;

        TypeVariableImpl(D genericDeclaration, String name, Type[] bounds) {
            disallowPrimitiveType(bounds, "bound for type variable");
            if (genericDeclaration == null) {
                throw new NullPointerException();
            }
            if (name == null) {
                throw new NullPointerException();
            }
            this.genericDeclaration = genericDeclaration;
            this.name = name;
            List<Type> types = new ArrayList<Type>();
            for (Type bound : bounds) {
                types.add(bound);
            }
            this.bounds = types;
        }

        public Type[] getBounds() {
            return toArray(bounds);
        }

        public D getGenericDeclaration() {
            return genericDeclaration;
        }

        public String getName() {
            return name;
        }

        public String getTypeName() {
            return name;
        }

        @Override public String toString() {
            return name;
        }

        @Override public int hashCode() {
            return genericDeclaration.hashCode() ^ name.hashCode();
        }

        @Override public boolean equals(Object obj) {
            if (NativeTypeVariableEquals.NATIVE_TYPE_VARIABLE_ONLY) {
                // equal only to our TypeVariable implementation with identical bounds
                if (obj != null
                        && Proxy.isProxyClass(obj.getClass())
                        && Proxy.getInvocationHandler(obj) instanceof TypeVariableInvocationHandler) {
                    TypeVariableInvocationHandler typeVariableInvocationHandler =
                            (TypeVariableInvocationHandler) Proxy.getInvocationHandler(obj);
                    TypeVariableImpl<?> that = typeVariableInvocationHandler.typeVariableImpl;
                    return name.equals(that.getName())
                            && genericDeclaration.equals(that.getGenericDeclaration())
                            && bounds.equals(that.bounds);
                }
                return false;
            } else {
                // equal to any TypeVariable implementation regardless of bounds
                if (obj instanceof TypeVariable) {
                    TypeVariable<?> that = (TypeVariable<?>) obj;
                    return name.equals(that.getName())
                            && genericDeclaration.equals(that.getGenericDeclaration());
                }
                return false;
            }
        }
    }

    static final class WildcardTypeImpl implements WildcardType, Serializable {

        private final List<Type> lowerBounds;
        private final List<Type> upperBounds;

        WildcardTypeImpl(Type[] lowerBounds, Type[] upperBounds) {
            disallowPrimitiveType(lowerBounds, "lower bound for wildcard");
            disallowPrimitiveType(upperBounds, "upper bound for wildcard");
            this.lowerBounds = JavaVersion.CURRENT.usedInGenericType(lowerBounds);
            this.upperBounds = JavaVersion.CURRENT.usedInGenericType(upperBounds);
        }

        @Override public Type[] getLowerBounds() {
            return toArray(lowerBounds);
        }

        @Override public Type[] getUpperBounds() {
            return toArray(upperBounds);
        }

        @Override public boolean equals(Object obj) {
            if (obj instanceof WildcardType) {
                WildcardType that = (WildcardType) obj;
                return lowerBounds.equals(Arrays.asList(that.getLowerBounds()))
                        && upperBounds.equals(Arrays.asList(that.getUpperBounds()));
            }
            return false;
        }

        @Override public int hashCode() {
            return lowerBounds.hashCode() ^ upperBounds.hashCode();
        }

        @Override public String toString() {
            StringBuilder builder = new StringBuilder("?");
            for (Type lowerBound : lowerBounds) {
                builder.append(" super ").append(JavaVersion.CURRENT.typeName(lowerBound));
            }
            for (Type upperBound : filterUpperBounds(upperBounds)) {
                builder.append(" extends ").append(JavaVersion.CURRENT.typeName(upperBound));
            }
            return builder.toString();
        }

        private static final long serialVersionUID = 0;
    }

    private static Type[] toArray(Collection<Type> types) {
        return types.toArray(new Type[types.size()]);
    }

    private static Iterable<Type> filterUpperBounds(Iterable<Type> bounds) {
        List<Type> types = new ArrayList<Type>();
        for (Type bound : bounds) {
            if (!bound.equals(Object.class)) {
                types.add(bound);
            }
        }
        return types;
    }

    private static void disallowPrimitiveType(Type[] types, String usedAs) {
        for (Type type : types) {
            if (type instanceof Class) {
                Class<?> cls = (Class<?>) type;
                if (cls.isPrimitive()) {
                    throw new IllegalArgumentException(String.format("Primitive type '%s' used as %s", cls, usedAs));
                }
            }
        }
    }

    /** Returns the {@code Class} object of arrays with {@code componentType}. */
    static Class<?> getArrayClass(Class<?> componentType) {
        // TODO(user): This is not the most efficient way to handle generic
        // arrays, but is there another way to extract the array class in a
        // non-hacky way (i.e. using String value class names- "[L...")?
        return Array.newInstance(componentType, 0).getClass();
    }

    // TODO(benyu): Once we are on Java 8, delete this abstraction
    enum JavaVersion {

        JAVA6 {
            @Override GenericArrayType newArrayType(Type componentType) {
                return new GenericArrayTypeImpl(componentType);
            }
            @Override Type usedInGenericType(Type type) {
                if (type == null) {
                    throw new NullPointerException();
                }
                if (type instanceof Class) {
                    Class<?> cls = (Class<?>) type;
                    if (cls.isArray()) {
                        return new GenericArrayTypeImpl(cls.getComponentType());
                    }
                }
                return type;
            }
        },
        JAVA7 {
            @Override Type newArrayType(Type componentType) {
                if (componentType instanceof Class) {
                    return getArrayClass((Class<?>) componentType);
                } else {
                    return new GenericArrayTypeImpl(componentType);
                }
            }
            @Override Type usedInGenericType(Type type) {
                if (type == null) {
                    throw new NullPointerException();
                }
                return type;
            }
        },
        JAVA8 {
            @Override Type newArrayType(Type componentType) {
                return JAVA7.newArrayType(componentType);
            }
            @Override Type usedInGenericType(Type type) {
                return JAVA7.usedInGenericType(type);
            }
            @Override String typeName(Type type) {
                try {
                    Method getTypeName = Type.class.getMethod("getTypeName");
                    return (String) getTypeName.invoke(type);
                } catch (NoSuchMethodException e) {
                    throw new AssertionError("Type.getTypeName should be available in Java 8");
                } catch (InvocationTargetException e) {
                    throw new RuntimeException(e);
                } catch (IllegalAccessException e) {
                    throw new RuntimeException(e);
                }
            }
        }
        ;

        static final JavaVersion CURRENT;
        static {
            if (AnnotatedElement.class.isAssignableFrom(TypeVariable.class)) {
                CURRENT = JAVA8;
            } else if (new TypeCapture<int[]>() {}.capture() instanceof Class) {
                CURRENT = JAVA7;
            } else {
                CURRENT = JAVA6;
            }
        }

        abstract Type newArrayType(Type componentType);
        abstract Type usedInGenericType(Type type);
        String typeName(Type type) {
            return Types.toString(type);
        }

        final List<Type> usedInGenericType(Type[] types) {
            List<Type> list = new ArrayList<Type>();
            for (Type type : types) {
                list.add(usedInGenericType(type));
            }
            return Collections.unmodifiableList(list);
        }
    }

    /**
     * Per https://code.google.com/p/guava-libraries/issues/detail?id=1635,
     * In JDK 1.7.0_51-b13, TypeVariableImpl.equals() is changed to no longer be equal to custom
     * TypeVariable implementations. As a result, we need to make sure our TypeVariable implementation
     * respects symmetry.
     * Moreover, we don't want to reconstruct a native type variable <A> using our implementation
     * unless some of its bounds have changed in resolution. This avoids creating unequal TypeVariable
     * implementation unnecessarily. When the bounds do change, however, it's fine for the synthetic
     * TypeVariable to be unequal to any native TypeVariable anyway.
     */
    static final class NativeTypeVariableEquals<X> {
        static final boolean NATIVE_TYPE_VARIABLE_ONLY =
                !NativeTypeVariableEquals.class.getTypeParameters()[0].equals(
                        newArtificialTypeVariable(NativeTypeVariableEquals.class, "X"));
    }

    private Types() {}

    public static boolean isAssignable(Class<?> lhsType, Class<?> rhsType) {
        if (lhsType.isAssignableFrom(rhsType)) {
            return true;
        }
        return lhsType.isPrimitive() ?
                lhsType.equals(Primitives.unwrap(rhsType)) :
                lhsType.isAssignableFrom(Primitives.wrap(rhsType));
    }
}
